POS0156 BONE DENSITY, MICROSTRUCTURE AND BIOMECHANICS OVER A 7-YEAR OBSERVATION PERIOD IN RHEUMATOID ARTHRITIS AND PSORIATIC ARTHRITIS - INFLUENCE OF AUTOIMMUNITY, DISEASE ACTIVITY AND BIOLOGICAL DMARD TREATMENT
Authors: S. Kemenes, K. Tascilar, A. Kleyer, I. Minopoulou, F. Fagni, A. Zekovic, C. A. Isnardi, A. M. Liphardt, S. Bayat, L. Schuster, G. Schett, D. Simon
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> Rheumatoid Arthritis (RA) and Psoriatic Arthritis (PsA) are characterized by a deterioration of bone mass, bone microstructure and biomechanics [1, 2]. However, little evidence is available on the long-term evolution of these bone properties and the impact of autoimmunity, disease activity and targeted anti-inflammatory therapy. <h3>Objectives</h3> To evaluate the longitudinal course of peripheral volumetric bone mineral density (vBMD), microstructure and biomechanics in patients with seropositive RA (RA+), seronegative RA (RA-) and PsA (i) by diagnosis (ii) disease activity and (iii) ever use of biologic/targeted synthetic (b/ts) DMARDs. <h3>Methods</h3> RA+, RA-, PsA patients who had at least one high-resolution CT scan were included. Prospectively collected longitudinal data from the distal radius. vBMD, microstructure and biomechanical properties were assessed and data on treatments and disease activity (DAS-28) were collected. We described and summarized the time course of these measurements, using linear regression models as age and sex adjusted time-conditional means and mean differences by disease category, time-varying weighted average disease activity and intervening b/tsDMARD treatments. <h3>Results</h3> We analyzed 946 scans from 412 patients (193 RA+, 68 RA-, 151 PsA) with a median CT follow-up duration of 24 months (IQR 0 to 47). (Table 1). Overall, bone quality showed a downward course over time. RA+ patients showed lower total and trabecular bone densities compared to patients with psoriatic arthritis throughout the time course. (Figure 1a). RA+ patients also showed decreasing trabecular number with increasing trabecular thickness, trabecular irregularity and trabecular separation over time in comparison to PsA (Figure 1 b) suggesting a gradual disappearance of the thinner trabeculae. We detected significant time/DAS-28 interactions in PSA patients indicating faster cortical bone loss over time with increasing DAS-28 (p interaction =0.049), in RA- patients showing faster trabecular bone loss over time with higher disease activity (p.interaction 0.044) and in RA+ patients for trabecular density (p interaction 0.038), bone stiffness (p interaction 0.022) and failure load (p interaction 0.034) indicating a faster deterioration of bone quality over time with increasing disease activity. Interestingly, RA+ patients exposed to b/tsDMARDs had numerically lower bone density compared to unexposed patients, whereas the temporal pattern suggested a more stable vBMD over time as opposed to a deteriorating pattern in the unexposed. However, the uncertainty in these analyses was large and none of the time-exposure interactions or pairwise differences over time between ever vs. never exposed categories were significant. <h3>Conclusion</h3> Autoimmunity impairs bone health over time and is particularly associated with impaired trabecular bone quality. Good control of disease activity in RA+, RA-, and PsA patients may be helpful in preventing bone loss and deterioration of bone microstructure, and biomechanics. Specific contribution of b/tsDMARDs to the time course of bone quality at the radius needs further clarification. <h3>References</h3> [1]Kocijan R et al. J Bone Miner Res 2015 [2]Stemmler F et al. Ann Rheum Dis 2018 <h3>Acknowledgements</h3> The study was supported by the Deutsche Forschungsgemeinschaft (FOR2886 PANDORA, CRC1181, CRC1483 EmpkinS). Additional funding was received by BMBF (project MASCARA), the ERC Synergy grant 4D Nanoscope, and the IMI funded projects RTCure and HIPPOCRATES, and the 2022 GRAPPA Pilot Research Grant (DS). <h3>Disclosure of Interests</h3> None Declared.